Rare elements in minerals of pegmatites of the Kolmozero deposit (Kola Peninsula)

Abstract

The content of rare elements in the mineral composition can vary over a wide range. Therefore, the distribution regularities of impurity elements in crystalline phases are used to solve various petrological problems. Rare elements in minerals are indicators of PT-conditions for mineral formation or late superimposed processes. Rare elements that do not form their own phases, but are completely dispersed as an isomorphic impurity in the grids of rock-forming minerals, serve as reliable indicators of the development of mineral formation processes. For the pegmatite process, such microelements are: Rb, Cs, Ba, Sr, Pb and Tl. The main rock-forming pegmatite minerals are represented by quartz, plagioclase, microcline, spodumene and muscovite. The content of rare elements: Li, Be, Ta, Nb, Cs, Rb, Mn, Ti, Hf, Sr, Ba, Tl, Pb, Th, U, Y, Zr, Zn, Sc, V, Cr, Co, Ni, Cu, Ga, Ge, As, Cd, Sn, Bi, W in spodumene, plagioclase, microcline and muscovite from rare metal pegmatites of the Kolmozero lithium deposit was determined by mass spectroscopy method with inductively coupled plasma (ICP-MS). A distinctive feature of the composition of spodumene is the high content of Li, Mn, Rb, Ti, Bi and Sn. In plagioclase high concentrations are noted for Li, Mn, Ti, Rb and Cr. According to the set of rare elements, microcline and plagioclase are comparable with each other. However, rare elements – V, Cr, Hf, defined in the plagioclase, are absent in the microcline. In comparison with plagioclase and microcline, muscovite is characterized by higher contents of Li, Ta, Mn, Ti, Be, Zn, Ga, Sn, Ba and Tl. The presence of a large number of rare elements in the composition of spodumene, plagioclase, microcline and muscovite may be due to isomorphism processes and the presence of mineral inclusions. High contents of Li, Be, Nb, Ta, Cs, Ti, Mn, Zn, Rb in the studied minerals indicate the enrichment of the pegmatite melt with these elements in the process of pegmatite formation.